This invention relates to cooling a fuel cell stack.
Fuel cells generate electrical energy by reacting two reactant gas streams with each other. One of the gases is referred to as an anode gas while the other is referred as a cathode gas. Certain fuel cells use a stream of gas that is rich in hydrogen as the anode gas and an air stream as the cathode gas. Each fuel cell includes an anode plate for introducing the hydrogen rich stream to the fuel cell and a cathode plate for introducing the air stream. A catalyst and a membrane, such as a proton exchange membrane, separate the anode plate and the cathode plate. When the fuel cell is in use, the catalyst splits hydrogen gas from the anode stream into protons and electrons. The protons pass through the membrane to react with oxygen from the cathode stream. The membrane does not allow electrons to pass through it, so the electrons cause the anode to become negatively charged while the protons cause the cathode to be positively charged, thereby generating a potential difference between the cathode and the anode. The potential difference can be used to provide electrical energy to a load. To maintain the ability of the membrane to allow protons to move through it, the membrane must be maintained in a moist state, for example, by humidifying the gases before they come into contact with the membrane.
Fuel cells generate electricity more efficiently when operated at an optimal operating temperature. The chemical reactions in the fuel cell typically generate heat. To maintain the fuel cell at the optimal temperature, a cooling system is used extract heat generated by a fuel cell. When fuel cells are operated in an environment where the temperature is below the optimal operating temperature, the reactant gases are preheated, for example to the optimal operating temperature, before they are introduced to the fuel cell.
Multiple fuel cells are typically stacked in series with the anode of one cell being electrically connected to the cathode of the next cell to generate larger potential differences between one end of the stack and the other end of the stack. The reactions in the fuel cells also generate heat. To maintain the fuel cell stack at a desired operating temperature, a cooling system is used to remove the generated heat from the fuel cell.
In general, one aspect of the invention relates to a fuel cell system that includes fuel cells, and cooling elements distributed among the fuel cells. The fuel cell also includes a first reactant intake manifold, a first reactant output manifold, a second reactant intake manifold, a second reactant output manifold, a cooling gas intake manifold, a cooling gas output manifold, and a liquid intake manifold. Each fuel cell includes an anode element, a cathode element, and an associated electrolytic member sandwiched between the anode and cathode elements. The electrolytic member and the anode element define a first reactant flow field through which during operation a first reactant flows from the first reactant intake manifold across a first side of the associated electrolytic member and into the first reactant output manifold. The electrolytic member and the cathode element define a second reactant flow field through which, during operation, a second reactant flows from the second reactant intake manifold across a second side of the associated electrolytic member and into the second reactant output manifold.
Each cooling element defines a coolant passage through which, during operation, a cooling gas flows from the cooling gas intake manifold into the cooling gas output manifold. Each cooling element also includes a liquid injection path through which during operation liquid from the liquid intake manifold is injected into the coolant passage to mix with the cooling gas passing therethrough.
Embodiments of the invention may include one or more of the following features. A conduit connects the cooling gas output manifold to the second reactant intake manifold and directs the coolant gas from the coolant gas output manifold to the second reactant intake manifold.
The fuel cell stack includes a cathode plate and an anode plate. The cathode plate has a cathode reactant surface and a cathode cooling surface opposite the cathode reactant surface. The cathode reactant surface forms the cathode element of a first fuel cell. The anode plate has an anode reactant surface and an anode cooling surface opposite the anode reactant surface. The anode reactant surface forms the anode element of a second fuel cell adjacent to the first fuel cell. The anode cooling surface is positioned against the cathode cooling surface to form a cooling element of the fuel cell stack. The cathode cooling surface defines a cooling channel which when positioned against the anode cooling surface forms the coolant passage.
The cathode plate includes a passthrough opening from the cooling channel on the cathode cooling surface to the cathode reactant surface. A liquid channel connects the passthrough opening to the liquid intake manifold. During operation, liquid from the intake manifold flows through the liquid channel and is injected into the cooling channel through the passthrough opening.
In general, a second aspect of the invention relates to a method that includes introducing a coolant gas into a channel defined within a fuel cell stack, introducing water into the channel so that the water hydrates the coolant gas to produce a hydrated gas, allowing the hydrated gas to flow along the channel to an outlet port, and allowing the hydrated gas to escape from the outlet port. The hydrated gas absorbs heat from the stack as it flows along the channel and removes the absorbed heat from the stack when it flows from the outlet port.
Embodiments of the second aspect of the invention may include one or more of the following features. The hydrated gas is directed to a reactive surface of the fuel cell, where it is reacted to generate electricity. The reaction produces a hydrated exhaust stream. Water is condensed from the hydrated exhaust stream by transferring heat from the exhaust stream. The condensed water is introduces into the channel at a pressure between one and 5 psi. to hydrate the coolant gas. The heat is transferred from the hydrated exhaust system to a residential heating system that, for example, heats air or water.
In general, another aspect of the invention relates to a cooling plate for use in a fuel cell stack that includes a coolant inlet port, which during operation receives coolant gas, a coolant outlet port; and a cooling surface. The cooling surface has a cooling channel leading from the coolant inlet port to the coolant outlet port. The coolant gas flows from the coolant inlet port through the cooling channel and out of the coolant outlet port. The cooling surface also includes a water inlet port that is connected to the cooling channel. Water is injected into the cooling channel during operation thereby hydrating the coolant gas to produce a hydrated gas. The hydrated gas absorbs heat from the first cooling plate as it flows along the cooling channel.
Embodiments of the invention may include one or more of the following features. The cooling plate includes a water manifold for providing water and a second surface opposite the cooling surface. The water inlet port runs from the cooling surface through the cooling plate to the second surface and the second surface has a water channel to direct water from the water manifold to the water inlet port. The second surface is a reactant surface that includes a reactive inlet port connected to the coolant outlet port to receive the hydrated gas, a reactive outlet port, and a reactive gas channel to allow the hydrated gas to flow from the reactive inlet port to the reactive outlet port. The reactive gas is reacted in the reactive gas channel to generate electricity.
In general, yet another aspect of the invention relates to a fuel cell system that includes a fuel cell stack, a heat recovery system and a conduit. During operation, the fuel cell stack generates electrical energy by reacting a first stream of reactant gas and a second stream of reactant gas. The fuel cell stack also produces a fuel cell exhaust stream that includes moisture. The heat recovery system is positioned to receive the fuel cell exhaust stream. During operation, the heat recovery system transfers heat from the fuel cell exhaust stream and causes the moisture contained within the exhaust stream to condense into water. The conduit is positioned to receive the condensed water. During operation, the conduit introducing the condensed water to the first stream of reactant gas in the fuel cell stack.
Embodiments of the invention may include one or more of the following features. The conduit provides enough condensed water to humidify the first stream or reactant gas. The fuel cell stack includes reactant channels and cooling channels. During operation, the first stream of reactant gas is reacted in the reactant channels. The first stream of reactant gas is flowed through the cooling channels before it is introduced to the reactant channels. An opening leads from the conduit to the cooling channels thereby allowing condensed water to flow from the conduit to the cooling channels.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.